Calculator
Deck Material Calculator
Size up deck boards, joists, footings and fasteners for your deck build.
Verified August 2026
Deck area
320 sq ft
- Decking (linear feet)
- 696 lf
- 16 ft boards needed
- 44 boards
- Joists
- 16 at 16" o.c.
- Footings
- 8
- Installed cost estimate
- $12,240 – $19,440
Estimates only. Local pricing, site conditions and code requirements change the real number.
The formula
Board count = deck area / effective board coverage; Joists = (deck width / spacing) + 1
A nominal 5/4" x 6" deck board covers about 0.46 sq ft per linear foot once the gap is included.
Worked example
A 16 x 20 deck is 320 sq ft — about 700 linear feet of decking, 14 joists at 16 in on center, and 9 footings.
Frequently asked questions
What joist spacing do I need for composite decking?
Most composite decking requires 16 inches on center for perpendicular installation and 12 inches for a 45-degree diagonal layout. Check the manufacturer's span table.
Sources
Sources & verification
Last verified August 2026. Cost figures are modeled estimates based on national baselines adjusted for local labor and material pricing — they are not quotes. Permit rules change; confirm with the building department before starting work.